The present invention relates to a method of forming a molded article and in one embodiment to a casting method wherein a resinous composition such as polyester or an epoxy resin is coated on the exterior surface of an article in order to provide a decorative surface as well as a liquid barrier to the article. In the past, either stainless steel or porcelain coated molds have been employed to provide the smooth surface on molded articles and coatings for castings and building materials including blocks such as concrete or cinderblock. The molding compositions are disclosed in U.S. Pat. Nos. 2,751,775; 3,328,231; 3,632,725, 4,031,289 and 4,329,822, the disclosures of which are hereby incorporated by reference and relied upon. However, the use of stainless steel molds in the production of a smooth coating on porous building blocks such as those disclosed in the first four of the aforementioned U.S. Patents has always resulted in the so-called "halo effect" upon curing of the resin. This appears as a non-uniformity in the form of a dull area in the surface of the molded material which is due to the non-uniform conductance of heat through the stainless steel mold.
To combat this non-uniformity in curing, it has been proposed to use a porcelain coated mild steel mold which, to a large extent, obviated this difficulty. However, the use of a porcelain coated metal mold suffers from the disadvantage that the useful life of such molds is unacceptably brief due to the fact that the porcelain easily became chipped or disfigured during use partially as a result of the rough handling of such molds by unskilled labor in the casting of the molded article. Various other coating techniques have been suggested, such as the electrolytic deposition of a coating metal on a metal substrate for the mold. While significant economies were realized, it has been found that the electrolytic deposition of a coating metal on a mold often resulted in adverse reaction with the molding compositions.
Accordingly, it is an object of the present invention to provide a method of molding a composition where the mold employed has been coated with an electroless deposition layer of a metal that is non-reactive with the resinous composition and the method of making a mold of the type used in the method of the present invention wherein nickel is electrolessly deposited on the interior surface of a metal mold where the mold metal itself is a mild steel the exterior surface is masked to prevent the deposition of the nickel thereon so that the exterior surface of the mold can be rendered, as by oxidation, uniformly receptive to heat whereby the heat will be uniformly dispersed to the molding composition while the composition is being cured. Further, the method of the present invention includes oxidizing the exterior surface of the mold to effect better heat absorption during the curing step.
To summarize the method of the present invention, a metal mold such as a cold or hot rolled steel or aluminum but preferably a mild steel metal mold that has its interior molding surface coated with a layer of nickel metal by an electroless deposition process is supplied with a resin composition in flowable form such as polyester resin or an epoxy resin which may contain a pigment and a filler such as sand. Next, a support member such as, for example, the surface of a building block is deposited in the mold and is coated by the resin composition. Support members such as those described in U.S. Pat. No. 4,328,822 may also be employed. Subsequently, the exterior surface of the mold is exposed to heat sufficient to cure the resin composition and to provide a secure attachment of the resin to the exterior surface of the support member. During curing, the composition will be hardened and be bonded to the support member such as the porous surface of a masonry unit.
After curing, the member with the resin material bonded to its surface, is removed from the mold and the mold is made ready for re-use.
With the method of the present invention, it has been found that the resulting product gives a uniform appearance to the molded composition without creating an adverse reaction with the mold surfaces, holes in the form or nonuniformities in the smooth surface.
In addition, the mold of the present invention can be repeatedly used during a substantially great number of curing operations than is possible with porcelain coated molds which offer the required repair or replacement after a single molding cycle.